The invention relates to a blade ring for air-swept roller mills having an outer ring and an inner ring, between which are positioned guide blades, accompanied by the formation of flow ducts.
Air-swept roller mills, bowl mills or also vertical air flow mills have grinding rolls rotatable about a fixed axis and which are placed on a rotary grinding bowl. Between the grinding bowl and the mill casing is formed an annular space, in which are positioned substantially radially oriented guide blades for guiding an upward carrier gas flow, e.g. an air flow, with which the ground material is supplied to a classifier. The annular space is constructed as an annulus and with the guide blades located therein is referred to as a blade ring and sometimes as a nozzle ring.
Known blade rings comprise a rolled, cylindrical or conical outer ring and inner ring or a combination of a conical outer or inner ring and a cylindrical inner or outer ring, between which are positioned the guide blades. The guide blades form flow ducts, which generally have a rectangular cross-section.
Apart from these blade rings comprising rolled rings and welded in guide blades, cast blade rings are also known.
The known blade rings are associated with relatively high manufacturing costs. In the case of large roller mills, which can have blade rings with an external diameter up to 7 m, additionally the transportation and installation are difficult to control and are costly. It is therefore known to segment the blade rings and to assemble in situ the individual segments or annular sectors. However, segmentation presupposes an annealing treatment, so that the ring structure is stress-relieved and separating cuts for producing the segments give rise to no deformation and in particular no cracking. Another disadvantage of known blade rings is that it is impossible to optimize the grinding and classifying process via the flow direction of the fluid introduced into the grinding chamber through the blade ring and the two-phase mixture of the fluid and the grinding material particles supplied to a classifier without dismantling the blade ring and fitting a blade ring with a different inclination of the individual guide blades.
In a blade ring known from DE 34 18 196 A1, the flow conditions are varied during mill operation by adjustably positioned outer ring segments. The guide blades are fixed and secured with an unchanged angle of inclination to the inner ring or inner ring segments and project outwards between terminal guidance and fixing parts. In the case of a maximum cross-section of the flow ducts, the horizontally adjustable outer ring segments extend up to the mill casing and in the case of a minimized cross-section to the guide blades.
A free annular space of the blade ring resulting from the travel of the outer ring segments, is disadvantageous because through this free annular space the fluid flow flows in such a way that it is not influenced by the inclination of the guide blades.
Another disadvantage is the lateral guidance and fixing parts, which define an outer ring segment and an inner ring segment and represent disturbing covers of the blade ring cross-section.